Microchannel reactor system for catalyst-assisted chemical reactions

Abstract

The invention relates to a microchannel reactor system for catalyst-assisted chemical reactions. Temperature and flow uniformity across the reactor is achieved through a multi-part microchannel design. Each microchannel is designed based on specific chemical reactions and is separated from other microchannels. It is located within a microchannel unit that can be optimized with high flexibility for temperature uniformity. The microchannels in the microchannel plates, together with recesses in the flow distributor plates and end plates, form a fluid flow network within the system. Further key advantages of the microchannel reactor system are its high compactness and compatibility with a wide variety of catalytic reactions.

Description

[0001] The present invention relates to a microchannel reactor system for catalyst-assisted chemical reactions, which is particularly suitable for catalytic reactions for the synthesis of chemicals and for catalyst testing. background

[0002] Microreactor technology has developed rapidly in recent decades. Since the dimensions of microreactors or microchannels are in the range of 10 -3 - 10 1Microchannel reactors, with their dimensions of just mm, offer inherent advantages such as short diffusion distances for mass and heat transfer, low pressure drop, and low concentration gradients. Therefore, microchannel reactors are widely used in fuel processes (Sabatier reaction, steam reforming, catalytic combustion, Fischer-Tropsch synthesis, hydrocracking, synthesis of dimethyl ether or hydrocarbons, etc.), materials synthesis (nanoparticles, organic compounds, polymers, and pharmaceuticals), and other applications.

[0003] The operating environment in a catalytically active microchannel is highly complex, as catalytic reactions are coupled with phenomena of mass and heat transfer and multiphase transformation. Therefore, a deeper understanding of such complex systems could shed light on other processes. For example, the catalytic methane / methanol conversion and Fischer-Tropsch synthesis, which employ Pt-, Pd-, Rh-, Cu-, Co-, Fe-, and Ru-based catalysts, are strongly exothermic reactions. The reactants / starting materials in most fuel processes are synthesis gases, while the products of Fischer-Tropsch synthesis and hydrocracking are in the liquid phase (i.e., olefins, diesel, wax, etc.).

[0004] The focus is on increasing the throughput of the catalytic microprocess, either by directly enlarging the dimensions of a single microchannel or by stacking, where multiple microchannels are combined in series or parallel. Stacking is considered the most practical approach, as the advantages of mass and heat transfer in an increased number of channels do not decrease dramatically compared to those in enlarged channels.

[0005] The biggest challenges in the development of catalytically active microchannels lie in two areas: thermal management and flow distribution.

[0006] 1) Thermal management is essential in catalytically active microchannels for operational reliability, catalyst longevity, and product selectivity. The heat of reaction from exothermic processes must be effectively dissipated from the microreactor to prevent uncontrolled temperature rises and catalyst sintering / deactivation, and to maintain optimal operating conditions for the entire loaded catalyst. For example, the selectivity of hydrocarbons for Fischer-Tropsch synthesis is temperature-dependent, and hot spots must be avoided to achieve low selectivity for C1 and high selectivity for C5+.Furthermore, the heat from the exothermic reactions from the individual microchannels tends to accumulate downstream when the process is scaled up by a higher number of microchannels; therefore, thermal management is essential for protecting the microchannels and for effective large-scale production.

[0007] The aim of configuring the microchannel reactors is therefore to achieve a uniform temperature distribution in order to operate the microreactor under optimal conditions for maximum catalyst utilization in safe and efficient production.

[0008] 2) Uniform flow distribution is crucial for microchannel expansion. Ideally, the mass and heat transfer properties within individual microchannels, as well as across all microchannels, are maintained during expansion. However, uneven flow within the microchannels is common, leading to spatial temperature variations and deviations in product selectivity. The more microchannels present, the larger the volume for cracking / recombination zones, resulting in a large overall volume for the microchannel reactor system. A flexible, compact, and cost-effective concept for improved flow distribution is desired. State of the art for individual microchannels

[0009] State-of-the-art microchannel reactors can be divided into two categories: single-channel reactors and multi-channel reactors. Single microchannels are suitable for laboratory-scale experiments because they do not require a flow distributor. Multi-microchannel reactors, on the other hand, are designed for high-volume production and generally require flow distributors and flow combiners.

[0010] The design of a single microchannel includes, among other things, determining its cross-section and channel length. There are various configurations for the cross-sectional geometry of a microchannel, e.g., rectangular, circular, trapezoidal, triangular, etc., and the size of its hydraulic diameter, d. h (see equation (1) has a magnitude of 10 -3 -10 1 mm. Due to the small dimensions, the temperature distribution in the cross-section is usually quite uniform. dh=4AP where A is the cross-sectional area of ​​the flow and P is the wetted perimeter of the cross-section. Depending on the purpose of the process, the length of the microchannel is determined by the residence time of the reactants and / or the total heat exchange capacity. The existing configurations of individual microchannels can be classified into i) cavity, ii) direct, iii) zigzag, sinusoidal, iv) serpentine, and spiral types. i) Cavity type

[0011] Cavity-like microchannels have an open cavity or an open cavity with embedded objects (e.g., columns), as described by L. Du and W. Hu [1]. The cross-sectional velocity profile under laminar conditions is nearly parabolic, indicating a strong non-uniformity of the flow profiles in the radial (i.e., cross-sectional) direction, which in turn leads to a non-uniformity of temperature. Furthermore, as the reaction progresses along the flow direction, there is a strong concentration gradient from upstream to downstream, resulting in an inherent non-uniformity of temperature in the axial (i.e., longitudinal) direction. Nevertheless, the pressure drop in cavity-like microchannels is generally small. ii) Direct type

[0012] The main characteristic of a direct-type microchannel is its straight main flow direction. Configurations of direct-type microchannels are discussed, for example, by M. Shaker et al. [2]. Complex cross-sections are used to increase flow turbulence compared to a straight channel with a uniform cross-section. The cross-sectional dimensions of direct microchannels are smaller than those of cavity channels, so radial inhomogeneity is not dominant. Although complex cross-sectional configurations can improve mixing and mass transfer, this comes at the cost of a higher pressure drop. Longitudinal temperature inhomogeneity is unavoidable due to the concentration gradient along the channel, resulting in a cold inlet region and a hot outlet region in exothermic processes. iii) Zigzag and sine type

[0013] In contrast to straight-type microchannels, zigzag and sinusoidal microchannels have a redirected main flow direction due to coiling. While the coil configuration facilitates mixing within the microchannel, these configurations differ from serpentine and helical channels (see section iv) below) because there is no direct heat exchange between the upstream and downstream portions of the channel. Therefore, zigzag and sinusoidal channels are comparable to straight-type channels in terms of heat exchange, and temperature unevenness along the channel persists. iv) Serpentine and spiral type

[0014] In contrast to zigzag and sinusoidal microchannels, serpentine and helical channels exhibit upstream and downstream heat exchange in some parts, resulting in a more homogeneous temperature distribution. Examples of serpentine and helical channels under the same heating conditions are given by Ravishankar and Prakash [3]. Due to the heat exchange between different parts of the channel, the temperature distribution of serpentine microchannels is uniform in the radial direction, while the inconsistency persists in the axial direction. A helical microchannel exhibits a better temperature distribution in both the axial and radial directions; however, the average temperature is higher due to the complex, intricate flow structure.

[0015] The biggest drawback of serpentine and spiral microchannels is that both types are quite long and exhibit a considerable pressure drop. A long channel is unnecessary, especially for fast catalytic reactions, as the reaction only takes place in a small area at the beginning of the microchannel. This leads to material waste and should be avoided in a scaling-up process. Furthermore, as described, the temperature distribution in the axial direction remains uneven in the serpentine type. The complex, intricate flow structure results in an increase in the average temperature within the spiral channel.

[0016] The uniformity of temperature is defined by a uniformity index of temperature U. T which is given by equation (2). UT=∫A⋅|T−Tavg|dA∫A⋅dA where T is the temperature and T avgThe average temperature of the entire microchannel reactor. A low value of U T This represents a high degree of temperature uniformity in region A. Temperature non-uniformity decreases for cavity, direct, zigzag, sinusoidal, serpentine, and spiral microchannels, necessitating strict thermal management for these configurations. However, the pressure drop values ​​for cavity, direct, zigzag, and sinusoidal microchannels are much lower than those for serpentine and spiral microchannels. v) Thermal management

[0017] Thermal management in individual microchannels is currently achieved primarily through the use of a jacketed heat exchanger and / or the strategic positioning of the catalyst. The jacketed heat exchanger surrounds the individual microchannel. Depending on the flow direction of the heat exchange medium, heat exchangers can be classified into co-flow and counter-flow configurations. Typically, the counter-flow configuration results in a high temperature differential (i.e., a non-uniform temperature distribution) but offers a high heat exchange capacity. In contrast, the co-flow configuration achieves a more uniform temperature distribution, albeit with a lower heat exchange capacity. Alternatively, the catalyst can be rearranged within the reactor (i.e., its position) to avoid temperature irregularities.Optimal catalyst positioning can lead to a more uniform temperature distribution in both co-current and counter-current configurations under the same operating conditions. However, it is important to note that the loading / positioning methodology can also be influenced by the reaction mechanism, the catalyst, and the operating conditions (especially the flow rate), so a balance between these factors and thermal management must be sought. A change in the flow rate can alter the hotspot position or the temperature distribution, necessitating readjustment of the catalyst position. Therefore, the major drawback of catalyst positioning for controlling the temperature distribution in microreactors is its lack of robustness. vi) Summary

[0018] Therefore, achieving a uniform temperature distribution in individual microchannels is difficult in practice, as the concentration profile along the channel is inherent to it. While channel configurations with serpentine and spiral shapes could facilitate heat exchange between the upstream and downstream portions of the channel, this comes at the cost of a higher pressure drop. Nevertheless, understanding the factors influencing the temperature distribution in a single channel can provide a useful guide for the configuration of multichannel reactors, which are of greater interest for increasing the conversion rate in chemical reaction processes. State of the art in multi-microchannels

[0019] Compared to simply increasing the size of the microchannels, scaling up the process ideally allows for the maintenance of mass and heat transfer advantages in each microchannel. Depending on the channel arrangement, existing multi-channel systems can be divided into two types: parallel and series channels. The characteristics of these two arrangements, heat exchange management, and the configuration of the flow distributor for multi-channel systems are discussed below. i) Parallel microchannels

[0020] The parallel arrangement of a certain number of microchannels results in a parallel multichannel reactor. Parallel microchannel configurations include parallel-direct, parallel-zigzag / sinusoidal, and parallel-serpentine / spiral. Practically speaking, the main characteristic of parallel microchannels is that they share a common inlet (i.e., also a flow distributor) and a common outlet (i.e., a flow combiner), resulting in a co-current arrangement. Parallel microchannels with counter-rotating arrangements (i.e., the flow direction of some channels is opposite) are rare due to the complexity of installing the inlets and outlets of multichannel reactors.

[0021] As mentioned in previous sections, the unevenness of the temperature distribution of a single channel is primarily caused by the concentration / temperature gradient between the inlet and outlet. In parallel-direct and parallel-zigzag / sinusoidal channels, this unevenness is further amplified when these channels are arranged in parallel, as the heat of reaction tends to accumulate at the downstream end. Therefore, large temperature differences across the entire multichannel reactor are unavoidable in parallel-direct and parallel-zigzag / sinusoidal designs.

[0022] In the parallel serpentine type, the temperature distribution in the radial direction is relatively uniform due to heat exchange between the channels, but heat accumulates downstream, resulting in a temperature gradient in the axial direction. In parallel spirals, the temperature uniformity in both the axial and radial directions is better due to heat exchange between the upstream and downstream channels. However, such a complex, interwoven flow structure is also found to increase the average coolant temperature. These two cases are discussed by Baek et al. [4]. Furthermore, the pressure drop in both the parallel serpentine and parallel spiral types is more than an order of magnitude greater than in the parallel direct type. ii) Serial-type microchannels

[0023] In the series-type reactor, the outlet of the microchannel(s) is connected to the inlet of the next series. Temperature and concentration could be "redistributed" between two series, for example, by heat and / or product removal before transport to the next series. However, this type of multichannel reactor is not common, as both the length and the total volume can be quite large for scale-up processes.

[0024] In summary, parallel-direct and parallel-zigzag / sinusoidal types exhibit poor temperature uniformity with low pressure drop; parallel-serpentine / spiral types show better temperature uniformity, but with a significant pressure drop, and parallel-spiral types in particular have a high average temperature due to their interwoven flow structure. Therefore, all these multi-microchannel systems require additional heat exchangers and effective flow distributors. iii) Thermal management

[0025] Existing thermal management methods for catalytic multichannel reactors mainly use parallel cooling channels for heat exchange around the microchannels. Typically, the catalytic microchannels are arranged parallel on a single plate, as are the cooling channels. Since this is the simplest and most compact configuration, three-dimensional catalytic microchannel reactors are constructed by alternately stacking the catalytic and cooling plates. The arrangement of the catalytic and cooling plates can be co-current, counter-current, or cross-current. An example of these three configurations, used for thermally coupled reforming of the methanol stream (i.e., cooling) and methanol / air combustion (i.e., heating), was discussed by Engelbrecht et al. [5].Similar to the jacketed heat exchangers for individual microchannels, the counterflow configuration carries the risk of catalyst damage due to overheating, as excessively high temperatures can occur, whereas the coflow configuration exhibits a smaller temperature difference with more moderate heat generation and lower heat consumption. The temperature difference and heat exchange capacity of the crossflow configuration lie between those of the counterflow and coflow configurations, and this configuration is frequently used in pilot-scale microchannel reactors.

[0026] In addition to the methods mentioned above, catalyst positioning is also used in multichannel reactors, particularly in coupled systems with exothermic and endothermic reactions. However, as already noted, the effectiveness of this method is highly dependent on operating conditions. Both careful reactor configuration and strict control of operating conditions are necessary to prevent thermal runaway. iv) Flow distributor / flow manifold

[0027] Another important aspect for the operation of multimicrochannel reactors is the configuration and installation of flow distributors. Existing flow distributor configurations can be divided into four types: chamber configuration, branching configuration, split-and-recombine configuration, and thick-walled screen configuration. (a) Chamber configuration

[0028] In this chamber configuration, the distribution and collection lines for all microchannel units are combined in a buffer chamber. Sometimes a baffle plate is installed in the chamber to better distribute the flow. The relative standard deviation of the flow rate σ Q (see equation (3)) of the chamber configuration is σ Q < 5%. The chamber configuration requires a sufficiently large flow range as a buffer, and a small chamber range usually results in a large deviation in the flow distribution. σQ=1Q¯1N−1∑j=1N(Qj−Q¯)2 where σ Q The relative standard deviation is N and Q j denotes the number of channels or the value of the flow rate in a specific channel j. (b) Bifurcation configuration

[0029] The bifurcation configuration is a simple and cost-effective method for splitting a fluid flow into several partial flows. The schemes of the most common bifurcation configurations were discussed by Liu and Peiwen Li [6]. A distributor widely used in fluid chemistry is the T-mixer, which splits the fluid flow into two flows (bifurcation). In the absence of a chemical reaction, σ Q < 5%, but σ QLess than 10% is acceptable during both manufacturing and installation. The other type of bifurcation is the internal flow configuration, where the splitting points are configured along with the microchannels, unlike T-mixers, which can be located outside the microchannel. However, the internal bifurcation configuration requires a large volume, and the pressure drop across the flow distributor can be more than 40 times greater than that in the reaction zone. Under reaction conditions, the internal bifurcation has σ Q < 3%. (c) Split-and-recombine configuration

[0030] The split and combined flow distributor can divide the flow into N (N=3, 4, ...) parallel channels and includes N-(N-1) / 2 branching points and (N-2)-(N-1) / 2 crossing points. However, the geometric parameters of each distributor channel between two branching / connection points must be carefully selected using the equivalent resistance model, and u Q < 5% could be achieved. An example of a split-and-recombine configuration was described by Tanaka, et al. [7]. (d) Thick-walled sieve configuration

[0031] A thick-walled sieve flow distributor is used to redirect the flows through multiple thick-walled sieves, which require even more space than microchannels, as shown by Rebrov et al. [8]. The disadvantage of this configuration is the large volume created by the flow distributor. Under reaction conditions (e.g., ammoxidation of ethylene at 550 °C), the thick-walled sieve configuration σ Q ≈ 2%. v) Summary

[0032] The main disadvantage of current flow distributor configurations is their large casing volume. In some cases, the flow distributor and flow collector together account for two-thirds of the total reactor volume. Furthermore, the relative standard deviation σ Q The existing flow distributors have an unacceptably high flow rate of around 5%, especially for precise catalyst analysis.

[0033] US patent 2002 / 0185184 A1 discloses a microchannel reactor system in which the system is constructed from stacked plates with different functions. These plates include, among others, flow channel plates, in which the microchannels are formed as recesses in the plates. The flow channel plates can be stacked on top of each other to create different flow paths, or a flow channel plate can be bounded by two coated plates with inlet and outlet openings. Inlet and outlet openings are also provided in the end plates.

[0034] A similar microchannel system is disclosed in DE 602 14 167 T2, which is designed for flow division and mixing.

[0035] Based on the above, the present invention relates to providing a microchannel reactor system with improved temperature and flow uniformity compared to the prior art, which is simultaneously compact and retains its advantages under different operating and reaction conditions.

[0036] These problems are solved by a microchannel reactor system for catalyst-assisted chemical reactions with the features of claim 1. Advantageous embodiments of the invention are specified in the corresponding dependent claims.

[0037] The microchannel reactor system for catalyst-assisted chemical reactions according to the invention comprises at least the features described below.

[0038] The microchannel reactor system comprises at least one microchannel plate, which in turn comprises at least four microchannels. The microchannels are formed as recesses in the microchannel plate, i.e., they are open on one or both sides (not at the edges) of the microchannel plate or are partially located within the microchannel plate. The two ends of the microchannels are arranged such that they lie within the plate; i.e., there is no recess extending to an edge of the plate. The microchannels are further characterized in that they have two terminal sections (including the two ends), which can be used as inlet or outlet, and a central section.

[0039] In one embodiment, the at least four microchannels are arranged in separate units of the microchannel plate. In this embodiment, the microchannel plates are formed by joining, and in particular reversibly joining, the units.

[0040] The microchannel reactor system further comprises at least two flow distributor plates with at least one recess—either as a channel or simply as an opening—that at least partially intersects the microchannels in the microchannel plate when they are stacked. This requires a corresponding arrangement of the recesses in the microchannel plates and flow distributor plates. The flow distributor plates can be designed with channels that are not formed as depressions, but rather as channels that lie completely within the flow distributor plates, which can also be described as a tube-like configuration. These internal channels have inlets and outlets at their ends leading from the flow distributor plates.Advantageously, the arrangement of the at least one opening of the flow distributor plates is designed with respect to its interaction with the microchannels in the microchannel plate such that it aligns with the terminal sections of the microchannels as an inlet or outlet. The arrangement can further be such that both terminal sections of a microchannel are captured by different flow distributor plates, i.e., from each side (top and bottom), as an inlet or outlet, meaning they align with these plates when stacked. For flow distributor plates with internal channels (tubes) within the plates, reversible stacking of both sides with respect to the microchannel plates is possible. The flow distributor plate can be designed with internal channels such that each microchannel in the microchannel plate is associated with a corresponding internal channel.In this design, the inlets and outlets of the channels in the flow distributor plates each coincide with a terminal section of a microchannel, regardless of the geometry, orientation, and / or stacking direction of the microchannel. This ensures a uniform flow distribution in each microchannel. The flow distributor plates thus include inlets and outlets that at least partially correspond to terminal sections of microchannels in the adjacent microchannel plate. The channels of the flow distributor plates are also advantageously designed with microchannel dimensions.

[0041] For catalytic reactions, the microchannels are coated with a catalyst at at least one interface. Interfaces are the walls forming the microchannels. An interface of the microchannels can be, for example, provided by one or two (an upper and a lower) flow distributor plates, which are at least partially coated with a catalyst on the side facing the microchannel plate and cover the microchannels as an upper or lower wall, and wherein the catalyst is at least partially coated on additional, reversibly arranged cover plates that are inserted between the microchannel and distributor plates. The coating of the cover plates is arranged at least such that a fluid flowing in the microchannels (a fluid, for the purposes of the invention, is a gas, a liquid, or a mixture of both) comes into contact with the catalyst.The cover plates can be configured to cover a single microchannel, more than one, or all microchannels of a microchannel plate. This allows for high flexibility in carrying out different catalytic reactions simultaneously in the same microchannel reactor system. The cover plates must be configured with regard to potential connections between the microchannel plates and adjacent flow distributor plates (see below for further details); that is, the cover plates may need to be shaped to allow flow from the flow distributor plate to at least one microchannel in the adjacent microchannel plate.Advantageously, the cover plate's recesses align with those of the adjacent flow distributor plate, allowing flow from an outlet of the flow distributor plate to pass through the cover plate into a terminal section of a microchannel in an adjacent microchannel plate. Conversely, flow from a second terminal section of a microchannel passes through another cover plate into an inlet of a flow distributor plate. The recesses, also referred to as openings, in the cover plates must be positioned so that they align with the corresponding inlets / outlets of the adjacent flow distributor plates and the terminal sections of the microchannel plates when stacked.

[0042] The microchannel reactor system is completed by two end plates, each with at least one full recess (opening) that can serve as an inlet or outlet for the channels or internal channels in the flow distributor plates. When stacked, the recesses in the end plates at least partially align with the channels in the flow distributor plates. Additionally, the end plates can be equipped with channels that are not recesses but rather channels formed by depressions in the plate or as internal channels (tubes) within the plates.

[0043] The listed components, which are at least part of the microchannel reactor system, such as the at least one microchannel plate, the optional cover plates, the at least two flow distributor plates, and the two end plates, are reversibly stackable. This last feature characterizes the reactor system as a modular system (at least one microchannel plate, the cover plates, the at least two flow distributor plates, and the two end plates). Modules with different functionalities can be stacked and assembled into a microchannel reactor system as needed for a specific reaction. The microchannels in the microchannel plate, together with the channels in the flow distributor plates and the recesses in the end plates, form a fluid flow network.The fluid flow network enables fluid flow from at least one recess in one end plate (inlet) to at least one recess in the other end plate (outlet), with the fluid flow network encompassing flow through each of the at least four microchannels in the microchannel plates. Depending on the intended application, it is not necessary to include all microchannels in the fluid flow network. The arrangement of various flow distribution plates, designed with different options for guiding the flow into the microchannel plates, offers numerous possibilities that can be selected according to requirements. Advantageously, the flow distribution plates direct the flow into the terminal sections of the microchannels, ensuring that the entire length is traversed and dead ends are avoided.

[0044] A particular aspect of the invention is that the microchannels are arranged such that each microchannel with a terminal section used as an inlet or outlet faces a central section or a terminal section with the opposite function of an adjacent microchannel. This arrangement places components with a higher temperature next to a component with a lower temperature in an adjacent microchannel, thus enabling better heat distribution. This arrangement allows the microchannel reactor system to be used for both exothermic and endothermic reactions.

[0045] For greater flexibility, the microchannel plates can also be assembled from several units, each containing one microchannel. The reversible and, in the case of rotationally symmetrical parts, rotatable stackability of the microchannel reactor system modules allows for individual customization by changing / tilting (reversing) / rotating only the at least one microchannel plate for a different flow regime or heat distribution within the plate, or by changing / tilting / rotating the cover plates to modify the catalytic reaction, or by changing / tilting / rotating the flow distributor plates to alter the flow direction, or by changing / tilting / rotating two of the three modules together, and / or together with changing / tilting / rotating parts of a microchannel plate, depending on the design. This is one of the advantages of the microchannel reactor system according to the invention.

[0046] A further advantage of the microchannel reactor system according to the invention is its flexibility, particularly with regard to the configuration of the microchannel plate. If the compatibility with the distribution plates is maintained by changing the microchannel configuration, switching between different microchannel plates for building the microchannel reactor system is easily accomplished.

[0047] In the microchannel reactor system according to the invention, the length of the microchannels in the microchannel plate is adjusted by the catalytic reaction conversion according to the following relationship according to equation (4): L=DaC0ufR where L is the length, Since the Damköhler number, which typically ranges between 1 and 100, C0 is the initial reactant concentration, u f where R is the flow velocity and R is the reaction rate.

[0048] In another embodiment, the microchannel plate is square. The square shape is advantageous not only in this embodiment but in all embodiments. The square shape simplifies handling and configuration, particularly with regard to calculating potential heat flows. However, the square shape is not mandatory, and other shapes such as rectangles in general, and even ovals, including circles, are possible. In this embodiment, the microchannels in the microchannel plate are arranged in the form of symmetrical serpentines. An embodiment in which each microchannel in the microchannel plate is arranged in a separate part, with the parts being assembled to form a microchannel plate, is also possible.The serpentine channels are arranged at 90° angles to each other and are each located in one quarter of the square. The terminal sections of the microchannels are positioned along one edge of the square unit and serve as inlets or outlets with respect to the flow directions in the fluid flow network. This demonstrates the high degree of flexibility in arranging different microchannel orientations within the four sections of the microchannel plate, while the flow distributor plate can uniformly distribute or collect the flows to or from the microchannels without further modifications. However, the serpentine shape is not mandatory. Other shapes, such as zigzag and spiral, are possible.In this arrangement with separate units, the heat of reaction from all microchannels in the case of an exothermic catalyzed reaction does not accumulate in parallel at the downstream end, as in other existing designs, but is redistributed: cold parts of one microchannel are located next to hot parts of an adjacent microchannel, thus balancing the overall heat distribution across the entire microchannel plate. Furthermore, such a serpentine arrangement within a microchannel itself allows for heat exchange between hotter and cooler parts of the microchannel. In this way, hot spots and overheating of the downstream part are avoided.

[0049] In endothermic reactions, heat should be added to the reaction, not removed. With such a uniform temperature control, made possible by the arrangement of multiple units, heat can be supplied evenly to the entire reactor, for example from a heating furnace, since the surface temperature of the reactor is similar. This ensures that the entire catalyst bed can be operated under the same and optimal conditions, resulting in high performance.

[0050] In another embodiment, the flow distributor plate is square, and a unit is arranged in each of the four quarters of the plate. Each unit comprises a channel with an "H"-channel configuration as a partial recess, meaning at most one side is open. The at least four ends are located in the same position near the four edges of the square unit as full recesses, oriented at 0°, 90°, 180°, and 270° from the center point. At least one end of the channel unit on the flow distributor plate coincides with an end of the microchannel unit on the microchannel plate. The "H" channel configuration is not mandatory; a "+" or "cross" or star-shaped configuration is also possible. However, the fluids should be directed towards the center of the channel unit and distributed evenly to the ends, or collected evenly from the ends to be discharged from the center of the unit.

[0051] In one embodiment, two or more microchannel plates are stacked. Each microchannel plate comprises at least four microchannels as complete recesses in the plate, with flow distributor plates inserted between the microchannel plates. In the configuration with closed sides, the flow distributor plates can be reversibly inserted between two microchannel plates, i.e., by inverting the plate. At least one end of a channel on the flow distributor plate corresponds to a terminal section of the microchannel unit on the microchannel plate, serving as the inlet of the microchannel, and at least one end of a channel on the inverted flow distributor plate corresponds to the other terminal section of the microchannel unit, serving as the outlet of the microchannel.Such a design and arrangement of flow distributor plates allows for different configurations and orientations of the microchannel units on the microchannel plate and even enables the application of various catalysts both laterally, i.e., on a single microchannel plate, and successively. This results in high flexibility for the parallel testing of a number of catalysts and offers the possibility of conducting different reactions in different microchannels.

[0052] Overall, the modular design of the microchannel reactor system presented here enables improved homogeneity of temperature distribution, allows for the reuse of individual components in different compositions, and offers flexibility regarding microchannel length and the reactions performed. Furthermore, it is a compact, space-saving configuration.

[0053] The stacks of units / modules in the microchannel reactor systems are sealed, for example, by high-temperature adhesives or by diffusion bonding. Examples include SteelMaster 43HT [9] and ceramic adhesive cement

[10] . Gaskets between the plates are applied using high-temperature gaskets, e.g., graphite-based

[11] , mica-based

[12] , or metal-based laminates

[13] . In addition to these examples, sealing can be achieved by using gaskets and clamps. Welding of certain parts or 3D printing of certain parts or the entire reactor is also possible. The latter, in particular, allows for flexible, reversible stacking and design options. A simulation was performed to estimate the influence of the sealing on temperature uniformity.The results show that the effect of the conductivity of the sealing materials on the temperature uniformity is within 2%, which suggests that the flexibility of the construction of multiple units / modules is not affected by the sealing / stacking materials and that common materials can be used for the microchannel reactor system according to the invention.

[0054] All module materials must be selected to meet the required thermal, chemical, and pressure stability under the expected process conditions, for which stainless steel is suitable. The channels and microchannels are manufactured using computer numerically controlled machining (including milling, turning, drilling, laser cutting, plasma cutting, and waterjet cutting), which is compatible with conventional stainless steel, or by additive manufacturing (including powder-based melting, blasting, and sintering of metal binders).

[0055] All features of all embodiments, modules, and parts of the microchannel reactor system outlined here are combinable. There is no limitation on the combinations that are given by mentioning them in an embodiment.

[0056] The microchannel reactor system according to the invention is particularly suitable for heterogeneously catalyzed gas-solid reactions, wherein the fluid in the fluid flow network is a gas. However, its use for heterogeneously catalyzed liquid-solid reactions is also possible, as are mixtures of gas and liquid flowing in the fluid flow network.

[0057] Exemplary embodiments of the invention are described below in conjunction with the figures.

[0058] The figures are attached to the claims and are accompanied by texts that explain individual features of the illustrated exemplary embodiments and aspects of the present invention. Each individual feature shown in the figures and / or mentioned in the text accompanying the figures can be incorporated (even in isolation) into any embodiment of the reactor system according to the invention. Fig. Exploded view of an exemplary stack of a microchannel reactor system showing the flow pattern of a series of microchannel units. (a) The flow pattern is represented by solid and dashed arrows; (b) hidden features of the plates are shown as dashed lines. Fig. Example of a microchannel plate with optimized heat distribution as a module of a microchannel reactor system. Fig. Exploded view of an exemplary stack of two microchannel plates connected via two flow distributor plates, intended for arrangement in a microchannel reactor. (a) The flow path is shown by solid and dashed arrows; (b) the hidden features of the plates are shown as dashed lines. Fig. (a) Detailed view of an exemplary interaction between a microchannel plate with four units and a flow distributor plate (with dashed line showing hidden features); (b) Fitting of the terminal sections of the microchannels of the microchannel plate with the flow distributor plate; (c) Example of an end plate configuration (with dashed line showing hidden features); (d) Sectional view of the end plate in (c).

[0059] In detail, it shows Fig. 1 Two perspective exploded views of the first embodiment of the microchannel reactor system according to the invention for catalyst-assisted chemical reactions 1, i.e., without / with dashed lines indicating hidden features. In this example, the stacking is as follows: end plates 2a, b, flow distributor plates 3a, b, c (cover plates are not shown separately in this case, or the flow distributor plates have partially internal channels), wherein the catalysts are coated on the flow distributor plates 3a, b, c on the sides facing the microchannel plate 4a, b. The flow distributor plates 3a, b, c have the same channel configuration; however, 3a, the upper one in the figure, and 3c, the lower one in the figure, have openings in the middle of four quarters facing the end plate 2a, b.Flow distributor plate 3b, the middle one in the figure, is reversed compared to 3a, while 3c is rotated 90° compared to 3a. The channels of the flow distributor plates each have openings at their ends serving as inlets and outlets. The microchannels in the microchannel plates 4a, b are complete recesses. The channels in the flow distributor plates 3a, b have two openings facing the end plate 2a, b. The corresponding modules (end plate 2a, b, flow distributor plates 3a, b, c, microchannel plates 4a, b) are shown in the exploded view by (a) solid lines (exposed parts) and dashed lines with arrows indicating the flow direction; and in . Fig. are the hidden characteristics that are in Fig. Areas not shown are represented by dashed lines.

[0060] The catalytic reaction for carrying out in the microchannel realtor system according to the invention is, in one example, the Fisher-Tropsch synthesis

[14] . The catalyst is a Co / Al₂O₃. 23 (Si) catalyst applied to the flow distributor plate using the wash-coating method. The flow velocities in the example reaction are 0.01 m / s (Reynolds number ~ 150). The microchannels are 4010 mm long, 638 mm wide, and 20 mm high. The microchannel profile from the internal simulation shows: U T =3.98, σ Q =0.17%.

[0061] In Fig. Figure 4 shows a detailed example of a microchannel plate 4 with optimized heat distribution as a module of a microchannel reactor system. Three microchannels are designed with the same serpentine geometry, with two of them oriented at 180° and 270° to the first. The fourth microchannel could then be configured with a different serpentine geometry. Since the inlet and outlet are fixed along one side of the square, various channel geometries are possible for the microchannel plate to optimize the temperature distribution, and the alignment with the flow distributor plates remains unchanged. The terminal sections of each microchannel face either the middle sections of the adjacent microchannels or the terminal sections, which must then be assigned the opposite function, so that the terminal sections used as inlets face the terminal sections used as outlets.

[0062] In Fig. An example is shown illustrating the adaptation of the inlets and outlets of only one microchannel 4a', 4b' in the microchannel plates 4a, 4b to the corresponding inlets and outlets 3b', 3c' of two adjacent flow distributor plates 3b, 3c according to Fig. and (b) shows. In this example, the serpentine shape is used for the two microchannels. The inlets and outlets of the microchannels 4a', 4b' are arranged along an edge of the respective microchannel plate. The channel design within the flow distributor plates 3b', 3c' corresponds to the configuration with an H-shaped channel as a partial recess. The lower flow distributor plate 3c' is tilted and rotated relative to the upper flow distributor plate 3b'. Such an arrangement allows for high flexibility in the design and orientation of the microchannel plate, i.e., 0°, 90°, 180°, 270°, while the inlets and outlets of the microchannel plates remain aligned. The arrow lines in exploded view (a) show the flow path, and the dashed lines in (b) show the features hidden in (a).

[0063] In Fig. Figure (b) shows an example of the inlet and outlet matching of a four-part microchannel plate with a corresponding flow distributor plate. In (a), an exploded view with dashed lines revealing hidden features shows a four-channel flow distributor plate (top image) where the four channels in the four quarters, each with four fully recessed ends, correspond, and a four-part fully recessed microchannel plate (bottom image). In (b), a stack / clamp view is shown where at least one end of the 'H' distributor channel in each quarter of the top flow distributor plate matches the inlet or outlet of each microchannel unit in one quarter of the bottom microchannel plate.The channel design and orientation of the microchannel units can be very flexible, and the incoming currents can be evenly distributed across four units regardless of the microchannel orientation. This system can be easily adapted to many purposes after optimization. Fig. Figure 1 shows an example of an end plate configuration. The channel is partially recessed into the plate; an opening in the center of the plate is impressed from the plate surface and reaches the partially recessed channel as the overall inlet or end outlet of the system, as shown in the sectional view in (d); four openings in the centers of four quarters of the plate are impressed from the other side of the plate and reach the partially recessed channel, which distributes or collects the flows to / from the centers of the distribution channels located on four quarters of the flow distribution plate, as shown in Figure 2. Fig.1 dargestellten Beispiel. Liste der Referenzen [1] L. Du und W. Hu. An overview of heat transfer enhancement methods in microchannel heat sinks, Chemical Engineering Science, Vol.:280, 2023, Pages 119081. https: / / doi.org / 10.1016 / j.ces.2023.119081 [2] M. Shaker, et al. Numerical investigation of laminar mass transport enhancement in heterogeneous gaseous microreactors, Chemical Engineering and Processing: Process Intensification, Vol.: 54, 2012, Seiten 1-11. https: / / doi.org / 10.1016 / j.cep.2012.02.001 [3] S. Ravishankar und K. Arul Prakash. Numerical studies on thermal performance of novel cooling plate configurations in polymer electrolyte membrane fuel cell stacks, Applied Thermal Engineering, Vol.: 66(1-2), 2014, Pages 239-251. https: / / doi.org / 10.1016 / j.applthermaleng.2014.01.068 [4] S. M. Baek, et al. A numerical study on uniform cooling of large-scale PEMFCs with different coolant flow field configurations, Applied Thermal Engineering. Vol.: 31(8-9), 2011, Seiten 1427-1434. https: / / doi.org / 10.1016 / j.applthermaleng.2011.01.009 [5] N. Engelbrecht, et al. Microchannel reactor heat-exchangers: A review of configuration strategies for the effective thermal coupling of gas phase reactions, Chemical Engineering and Processing - Process Intensification, Vol.: 157, 2020, 108164. https: / / doi.org / 10.1016 / j.cep.2020.108164 [6] H. Liu und Pewen Li. Even distribution / dividing of single-phase fluids by symmetric bifurcation of flow channels, International Journal of Heat and Fluid Flow, Vol.: 40, 2013, Pages 165-179. https: / / doi.org / 10.1016 / j.ijheatfluidflow.2013.01.011 [7] Y. Tanaka, et al. Detection and diagnosis of blockage in parallelized microreactors, Chemical Engineering Journal, Vol. 167(2-3), 2011, Pages 483-489. https: / / doi.org / 10.1016 / j.cej.2010.09.087 [8] EV Rebrov, et al. Header configuration for flow equalization in microstructured reactors, AIChE Journal, 53(1), 2006, pages 0001-154. https: / / doi.org / 10.1002 / aic.11043 [9] Epoxy adhesives for bonding stainless steel. https: / / www.masterbond.com / applications / epoxy-adhesives-bonding-stainless-steel. (Accessed: 21.08.2024)

[10] High-temperature adhesives. https: / / www.final-materials.com / gb / 206-high-temperature-adhesives. (Accessed: 21.08.2024)

[11] GraFoil ® Flexible Graphite. https: / / www.neograf.com / Products / Gaskets-Sealants / grafoil-flexiblegraphite. (Accessed: October 11, 2024)

[12] Klinger Milam PSS. https: / / www.klinger.co.uk / storage / app / media / Product%20Specifications / Jointing%20materials / Milam%20PSS.pdf. (Accessed: 11 October 2024)

[13] Klinger graphite laminate sheets. https: / / www.klinger.co.uk / products / jointing-materials / klingergraphite-laminated-sheeting. (Accessed: 11 October 2024).

[14] A. Rai, et al. Kinetics and computational fluid dynamics study for Fischer-Tropsch synthesis in microchannel and fixed-bed reactors, Reaction Chemistry & Engineering, Vol.: 3(3), 2018, Pages 319-332. DOI: https: / / doi.org / 10.1039 / C8RE00018B

Claims

[1] Microchannel reactor system for catalyst-assisted chemical reactions (1), comprising at least: a. a microchannel plate comprising at least four microchannels as recesses in the plate, the ends of which are located inside the plate, and each having two terminal sections that can be used as an inlet or outlet, and a central part, b. two flow distribution plates, each comprising at least one channel as a recess, which in the stacked state at least partially meet the microchannels in the at least one microchannel plate; c. two end plates, each with at least one complete recess as an inlet or outlet; d. and wherein the microchannel plate, the flow distributor plates and the end plates are reversibly stackable and the microchannels in the microchannel plate together with the channels in the flow distributor plates and the recesses of the end plates form a fluid flow network and wherein the microchannels are coated with a catalyst at least at one interface and the microchannels are arranged such that each microchannel with a terminal section used as an inlet or outlet faces a central part or a terminal section with the opposite use of an adjacent microchannel e. and the microchannels are at least partially closed on both sides with cover plates as additional parts of the microchannel reactor system, wherein the cover plates are coated with a catalyst on one side facing the microchannel plate. and whereby The length L of the microchannels in the microchannel plate is set by the catalytic reaction conversion according to the following relationship: L=DaC0ufR where L is the length, since Damköhler's number is in the range of 1-100, C0 is the initial reactant concentration, u f the flow velocity and R the reaction rate. [2] The microchannel reactor system (1) according to claim 1, wherein the microchannel plate is rectangular and the microchannels have the form of symmetrical serpentines and the serpentines are arranged rotated by 90° to each other and wherein the terminal sections of the microchannels are alternately provided between the serpentines themselves as inlets or outlets with respect to the flow directions in the fluid flow network. [3] The microchannel reactor system (1) according to claim 1, comprising two or more microchannel plates, and wherein each microchannel plate comprises at least four microchannels as recesses in the microchannel plate, and wherein the microchannel plates have matching positions for their terminal sections to be used as inlet and outlet, respectively, and wherein the microchannels of each microchannel plate are at least partially closed on both sides with removable cover plates, and wherein the cover plates are coated with a catalyst at least on each side facing a microchannel plate.

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